1. Technical Field
The present invention relates to a piezoelectric vibrator, intrinsic frequency adjusting method of a piezoelectric vibrator, a piezoelectric actuator and an electronic device
2. Related Art
In view of excellent conversion efficiency from electric energy to mechanical energy and high responsivity of piezoelectric element, a piezoelectric actuator that drives an object by transmitting a vibration of a piezoelectric vibrator having a piezoelectric element has been recently developed.
Known piezoelectric vibrator used for the piezoelectric actuator is shaped in a rectangular or trapezoidal plate or stick, which is vibrated in mixed vibration mode of longitudinal primary vibration and bending secondary vibration. Predetermined frequency of alternate voltage is applied to the piezoelectric element to resonate the vibrator and an object such as a rotor is highly efficiently driven in tangential direction of ellipsoidal locus traced by a part of the vibrator.
Conventional support member for supporting the vibrator in a vibratable manner while being in contact with the rotor is a narrow section or a linear beam member provided on a lateral side of plate-shaped vibrator at a position near nodes of longitudinal vibration and bending vibration. Since the vibrator is supported at lateral side, the thickness of the piezoelectric actuator can be reduced (see, for instance, Document 1: Japanese Patent No. 3,614,009 (FIG. 1)).
As an alternative, narrow section and an L-shaped spring section for urging the vibrator toward the rotor are integrated to form a support (see, for instance, Document 2: Japanese Patent No. 3,721,928 (FIG. 2 etc.)).
As described above, conventional support member supports the vibrator at a position adjacent to vibration nodes where displacement per each vibration mode is minimized, thereby avoiding restriction on the vibration of the vibrator.
Intrinsic frequency (i.e. resonance frequency) of the piezoelectric vibrator is likely to be deviated in accordance with deviation of the properties of piezoelectric material, machining dimension of component and assembly error. In order for a part of the piezoelectric vibrator to assume an ellipsoidal movement, the intrinsic frequency of the longitudinal vibration and the bending vibration has to be adjusted to satisfy a predetermined relationship.
The above-mentioned support member is used for adjusting the intrinsic frequency, which is carried out by, for instance, cutting the support member. However, when a vibrator having mixed mode of vibration, i.e. longitudinal vibration and bending vibration is used, it is preferable to separately adjust the intrinsic frequency per each vibration mode considering efficiency in adjustment process.
However, since the bending vibration is a point-symmetric vibration around the center of gravity of the vibrator, which accompanies the moment in a displacement direction of the longitudinal vibration, the support member provided on the lateral side of the vibrator is bent in the longitudinal direction of the vibrator, thereby applying the moment on the support member. In other words, in addition to the displacement on account of the longitudinal vibration and the bending vibration, the moment is also applied on the support member. Accordingly, even when the support member does not have a narrow shape or a beam shape but has an L-shape, and can be cut at both ends, intrinsic frequency of longitudinal vibration and intrinsic frequency of bending vibration cannot be separately adjusted. Accordingly, it is extremely difficult to adjust the intrinsic frequency, where productivity and yield rate are deteriorated to result in high production cost.